In modern variable displacement hydraulic systems, it quite often becomes necessary to provide an order of priority for the pump output, since the pump cannot supply all of the circuits of the system with their maximum flow requirements at the same time. For example, the power steering circuit of a mobile system must have priority over the other circuits of the system. Another example would be in a combine system where the reel motors must have priority over certain other functions. Likewise, the remaining functions may also require priority over each other so that each function of the system might have a different priority.
One method of providing priority flow based on pressure would be the use of a relief valve downstream of the priority function, or another similar method would be to vary the spring force on the load checks of a conventional valve. Another prior art method of obtaining priority flow would be the use of a flow divider valve such as taught in U.S. Pat. No. 3,229,717.